1. Field of the Invention
The present invention relates to an audio signal processing apparatus and a method for processing audio signals in such a manner that audio signals corresponding to predetermined sound sources are removed from time-sequential audio signals of first and second systems, wherein the time-sequential audio signals are constituted of audio signals from a plurality of sound sources.
2. Description of the Related Art
Phonograph records and compact disks record sound as stereo audio signals of left and right channels. The audio signals of the left and right channels are often generated from a plurality of sound sources. Often, the levels of the stereo audio signals in each channel are differed so that, when the stereo audio signals are played using two speakers, sound images of the sound sources are localized at positions between the speakers.
For example, if signals S1 to S5 from five sound sources 1 to 5, respectively, are recorded as a left-channel audio signal SL and right-channel audio signal SR, the signals S1 to S5 may be additively mixed within the audio signal SL and SR at different levels so that the audio signal SL and SR are represented as:SL=S1+0.9S2+0.7S3+0.4S4 andSR=S5+0.4S2+0.7S3+0.9S4.
If the above-described typical stereo audio signals of two channels include a singing voice and instrumental music, by removing the singing voice from the audio signals, the instrumental music having the singing voice removed can be used for a karaoke machine.
FIG. 18 is a block diagram illustrating the structure of such a singing-voice removing apparatus. In stereo music, the singing voice is normally localized in the middle of the other sounds of the left and right channels. Therefore, the singing voice can be removed from the stereo audio output by subtracting the left-channel audio signals from the right-channel or vice versa in the singing-voice removing apparatus illustrated in FIG. 18.
In FIG. 18, the above-described principle is only applied to the audio band for the singing voice. The left-channel audio signal SL and the right-channel audio signal SR are sent to a subtracting circuit 1 and to band-stop filters 2 and 3 for removing frequency band components corresponding to the audio band for the singing voice (for example, 300 Hz to 5 kHz). Then, the result of subtracting the left-channel audio signals from the right-channel or vice versa output from the subtracting circuit 1 is sent to a band-pass filter 4 for separating the frequency band components corresponding to the audio band for the singing voice.
The output signal from the band-stop filter 2 and the output signal from the band-pass filter 4 are added at an adding circuit 5 to obtain a left-channel output signal SOL not including the audio components corresponding to the singing voice. The output signal from the band-stop filter 3 and the output signal from the band-pass filter 4 are added at an adding circuit 6 to obtain a right-channel output signal SOR not including the audio components corresponding to the singing voice.
For further details, refer to Japanese Unexamined Patent Application Publication No. 2000-354299.